There are many applications that require air to be diffused throughout large containers of liquid, typically water. An example of such an application is the aeration of contactors, which are most often used in processing, cleaning, purifying, or otherwise treating wastewater. Applicant's invention may be used for general aeration services but is particularly well suited for aerating contactors.
Aeration, effecting intimate contact between air and liquid, is widely used for the purpose of dissolving oxygen to support aerobic organisms employed in wastewater treatment and agitation or mixing to suspend and prevent sedimentation of solids. Some popular models of contactors are "air driven" devices wherein the air moving through the media drives the contactors, thus eliminating the need for mechanical gear and motor drives.
An air diffusion apparatus incorporating applicant's invention accomplishes the oxygen dissolving function by diffusing low pressure air into wastewater through orifices in a perforated pipe or specialized diffuser nozzles in a diffuser header, so that small bubbles are discharged uniformly into and rise continuously through the wastewater.
There are many reasons why an efficient method of aerating contactors is needed. Added transfer of oxygen into the wastewater increases system treatment capacity and efficiency by creating an environment favoring beneficial biota and reduced nuisance growth. Certain advanced and combined treatment processes with contactors require aeration for successful operation. A thinner biomass is achieved and maintained through increased agitation as the air bubbles rise through the contactor media. Thinner biomass reduces structural loads on the contactor and contactor support shaft, and reduces hydraulic drag as the contactor rotates in the wastewater, thus potentially reducing energy consumption and permitting closer spacing of the contactor media with less risk of mechanical overloading from excessive biofilm growth. Increased concentrations of wastewater can therefore be applied to aerated contactors. Tests have demonstrated up to 50% greater loadings and removal efficiencies. Aeration in the lower portion of the contactor tank assists in keeping solids in suspension. These and other reasons make desirable an efficient aeration method.
There are numerous designs and configurations for submerged diffused aeration devices. However, when there is a contactor or other obstruction in the tank, positioning the aeration device correctly in the tank can be difficult. Additionally, because the devices carry air through a heavier liquid, buoyancy can be a problem. There are designs that embrace ballast or weights to prevent flotation, but no known prior art device combines weight to prevent flotation with rolling or sliding shoes for positioning, support, and mobility of aeration headers.
Prior art contactor aeration devices are typically attached mechanically to the bottom of a contactor tank and to the to of the tank walls. Traditional methods of support and anchoring such devices require fixed support, hooks, or brackets, all mounted with anchor bolts to the tank floor or walls. These methods require installation before the contactor is put in lace, making the aeration device difficult to remove for service and almost impossible to relocate if adjustment of position is indicated.
Accordingly, one object of applicant's invention is to make possible an aeration system that allows convenient installation and removal of an air diffusion system apparatus in new or existing tanks containing contactors or variants thereof, or containing other obstructions.
Another object of this invention is to prevent flotation of the pipes and diffuser header assemblies without using fixed support, hooks, or brackets mounted to the tank floor or walls, by making diffuser header assemblies that are negatively buoyant when installed and while in use.
Applicant's invention solves these and other problems by providing structure that uses novel means for supporting and locating the apparatus on the tank floor, and preventing flotation with added weight, preferably by a plurality of weighted shoes.
An air diffusion apparatus comprising applicant's invention features an air supply manifold, one or more "drop pipes" (with or without air control valves) connected to the air supply manifold, and one or more negatively buoyant diffuser header assemblies connected to respective drop pipes and preferably containing one or more shoes. Each diffuser header assembly provides one or more diffuser orifices comprising nozzles or holes.
The shoes are preferably weighted, can slide or rotate along tank surfaces, and are preferably located on the diffuser header, which is essentially a pipe through which air can flow toward an end cap. The end cap can host an additional diffuser orifice outboard of the shoe, and acts as a "bumper" should it contact a tank wall or the like during installation. Air control valves on individual drop legs, and coarse bubble diffusers, may be furnished as an option for flexibility in air control.
The drop pipes are carefully designed and configured depending on the shape and configuration of the tank and obstruction, in order to allow easy installation and removal of the diffuser headers without interference with the contactor or tank wall. The drop pipes deliver air to the diffuser headers, which distribute air along the tank through the diffuser orifices.
Submerged air diffuser devices, depending upon the size and weight of piping, tend to be buoyant when the tank is filled with liquid and the pipe is filled with air. This problem is overcome in the referred embodiments of applicant's invention by using weighted shoes to locate the diffuser header at the desired elevation for best operation while allowing clearance underneath a contactor or other obstruction, and providing sufficient weight to prevent flotation of the aeration equipment. Other embodiments can be made with the weight or weights placed at other locations about the diffuser header, but it is referred to use weighted shoes, so that the shoes themselves comprise sufficient weight or have weights attached or placed adjacent to them. When the air diffusion apparatus is being installed in or removed from a tank, the weighted shoes keep the apparatus from floating, while allowing mobility by rolling or sliding along the tank bottom or inclined walls. This minimizes the force necessary to lift and move the device, while preventing unnecessary strain on piping and joints associated with less freely rolling or sliding devices.
Shoe is used herein to mean any structure (wheels, rollers, runners, bearings, etc.) for supporting a device while allowing it to safely and conveniently roll or slide against the side or bottom of a tank. Weighted shoe (weighted runner, weighted roller, etc.) is used herein to mean either a shoe (runner, roller, etc.) that is itself heavy or weighted, or a shoe (runner, roller, etc.) placed in close proximity to a weight or weights. Pipe sections may be plastic, steel, stainless steel, other metals, or any other suitable materials, fabricated with screwed fittings, solvent welded fittings, welded metal fittings, adapters or sections formed by bending or rolling, or by any other suitable means. Connections may be flanged, screwed, unions, mechanical joints, or any other suitable type.
One advantage of applicant's invention is adjustability. The diffuser header can be accurately positioned or relocated within the tank by adjustments made above the tank walls, using the drop pipe as a tongue or handle.
Another advantage of the invention is that, as mentioned previously, it provides for use of a hollow shaft or pipe as a support for the shoes. This feature allows one or more aeration ports or diffuser orifices to be mounted outboard of the shoes, thereby providing greater aeration width and eliminating dead spaces at the end of the diffuser header. This feature also helps avoid interference with tank walls and damage to diffuser assemblies.
A further advantage of the invention is improved convenience of installation and (when necessary) removal of the diffuser header, saving substantial time and cost in construction or retrofit of such systems. In systems that require a fixed floor-mounted submerged bracket, the upper piping must be adjusted to comply with that inaccessible bracket. But with the rolling or sliding shoe feature of the invention, normally only the piping above the tank needs to be adjusted when installing.
Advantages of applicant's air diffusion apparatus include convenience and ease of installation in new or existing tanks. Applicant's air diffusion apparatus can be installed with tanks full of wastewater and contactors in place, immediately providing the advantages of contactor aeration. The weighted shoes allow easy installation and adjustment of applicant's air diffusion apparatus, and anchoring and control is all conveniently located above the wastewater surface.